Downton Abbey survived World War I. But can the country manor weather the latest skirmish, a below-stairs battle between those scheming servants O'Brien and Thomas?That's just one of the many entertaining questions and diverting dilemmas presented by the long-awaited - and well worth the wait - third season of this Masterpiece Classic addiction, which returns like a delicious if bittersweet bonbon. (And how I hope you've kept the blinders on regarding the many spoilers issuing from across the pond during the recent U.K. telecast.)"No family is ever what it seems from the outside," muses the formidable Dowager Countess (the peerless Maggie Smith) during one of the many crises that beset the Crawleys and their loyal servants over the next seven Sundays (PBS, check tvguide.com listings). That fact is one of the primary draws of this deluxe period soap opera, which revels in heightened stories of secrets, setbacks and scandals that could shake Downton to its foundation, with passion and stiff-upper-lip resilience sustaining these characters, who have become to feel like family, through episodes of tragedy and uncertainty in changing times.The big event in this Sunday's two-hour opener, besides the impending nuptials of Matthew and Lady Mary, is the arrival of the legendary Shirley MacLaine as Countess Cora's wealthy mother, Martha Levinson, an American force of bossy nature who preaches a gospel of modernity, of embracing the 1920s and not clinging to the values of a vanishing past. "These houses were built for another age," she declares, a sentiment that naturally doesn't endear her to the Dowager (who sniffs, "When I'm with her, I'm reminded of the virtues of the English"). Watching Shirley and Dame Maggie face off is a delight, but Downton isn't Dynasty, so don't come expecting an actual catfight.Martha's too-fleeting appearance, during which social barriers are shattered during a calamity-prone dinner party, sets the stage for a showdown between young visionary Matthew and tradition-bound Robert, the Earl of Grantham, over the financial future and management of Downton. (Dan Stevens and Hugh Bonneville are at their best in these moments.) "The post-war world is not being kind to him," observes Robert's sympathetic wife Cora (Elizabeth McGovern), who nevertheless chides her mate, "You're always flabbergasted by the unconventional."There's plenty of opportunity for that, as the Earl must contend with an Irish rebel son-in-law (Allen Leech, whose role grows stronger as the story develops) and a restless middle daughter with journalistic ambitions (Laura Carmichael as the unlucky-in-love Lady Edith), while his conservative counterpart below, head butler Mr. Carson (Jim Carter), wrangles an unruly staff upended by the addition of two young head-turners. Adding to the fun: a malicious vendetta between former pals O'Brien (Siobhan Finneran) and Thomas (Rob James-Collier), whose homosexuality becomes a provocative plot point for many of the later chapters.Downton Abbey is like British catnip, a dazzling entertainment where saucy always trumps stuffy. It's popcorn TV with a champagne aftertaste. (If you can't get enough, tune in an hour early for Secrets of Highclere Castle, a special revealing the history of the actual edifice where Downton is set. Did you know it served as a WWI military hospital, just like Downton? Now you do.)Want more TV news and reviews?Subscribe to TV Guide Magazine now!SECRETS IN AMISH COUNTRY: The chill sets in early. And not just because a young girl's mutilated body in a snowy field seems so gruesomely out of place in the quaint Amish countryside. In the Lifetime movie An Amish Murder (Sunday, 9/8c), new police chief Kate Burkholder's investigation is further complicated by the frigidly cold shoulder she gets from the locals. Kate, you see, grew up Amish in Painter's Mill, Ohio, the small town to which she has returned after 15 years as a big-city detective.Having abandoned her rigidly traditional upbringing, Kate now lives "under the ban" from the Amish, including her own family members, who shun her and can barely look at her. Even questioning suspects from that community can require a go-between. It's a compelling situation for an above-par procedural, this one adapted from the first book in Linda Castillo's series of mystery novels, Sworn to Silence, which is a more thoughtful and meaningful title than the generic An Amish Murder.Neve Campbell (most recently seen as one of Derek's strong-willed sisters on Grey's Anatomy), plays Kate, and is better at conveying the tremulous pain of her personal alienation than she is at credibly barking orders with authority as the town's top cop. Which is okay, because the mystery plotting feels rather mechanical anyway.What makes this Murder intriguing is the context of a closed society that protects even its deadliest secrets from the intrusion of the modern "English" interlopers. This culture clash helped make the Oscar-winning Witness a hit in 1985. If Amish Murder does well, I wouldn't be surprised to see a series of sequels further immersing Kate in the world she left behind. By the end of this first chaper, there's even a hint of a thaw.COMEDY NIRVANA: With a droll and deft touch of satirical affection for the obsessive oddball in all of us, Saturday Night Live's Fred Armisen and partner-in-whimsy Carrie Brownstein have made Portland, Oregon, a destination for quirkily ironic absurdism. Their Peabody-winning Portlandia begins its third season Friday on IFC (10/9c) with a hodgepodge of vignettes that tweak trendy pastimes and topics including yoga meditation, dairy alternatives (zucchini milk?) and unemployed-millennial angst.The opener's high point is an extended sketch in which armchair activist Spyke and girlfriend Iris embark on a crusade to "take back MTV" from the non-musical tyranny of shows like My Super Sweet 16. "Do people even know about rocking the vote anymore?" Iris laments. Enlisting Kurt Loder ("I can be sardonic") and other former MTV luminaries in their cultural revolution, these Portlandia geeks rock it with eye-rolling fervor. As 30 Rock's Liz Lemon has been known to say, "I want to go to there."WHAT ELSE IS ON FRIDAY: High stakes on ABC's Shark Tank (9/8c), as sharks Mark Cuban and Lori Greiner make a $1 million offer after hearing one of the pitches. Hitch: It's for 100 percent of the start-up. ... The possibility of underwater riches tempts the dredgers of Nome, Alaska, as a second season gets underway of Discovery's Bering Sea Gold (10/9c). ... On CBS' Blue Bloods (10:02/9:02), a family tragedy distracts Danny (Donnie Wahlberg) from his search for a sniper who's targeting drivers of gas hogs. ... As Syfy's Merlin begins its fifth and final season (10/9c), the title wizard (Colin Morgan) must try to keep Camelot and King Arthur's court from succumbing to its legendary fate.WHAT ELSE IS ON SUNDAY: Give ABC's Nashvillecredit for trying to round up new fans any way it can. In preparation for the show's return with new episodes this Wednesday (10/9c), a marathon of key repeats will air on CMT, starting at 2 pm/1c. ... ABC's prime-time lineup returns from holiday break, minus 666 Park Avenue, which is on permanent hiatus (though the remaining episodes are expected to air this summer). On Once Upon a Time (8/7c), Regina is accused of murder, and only Emma seems to think she didn't do it. On Revenge (9/8c), Emily has a new target, and we can only hope it will be more interesting that what she's been up to lately. And in place of 666, we get bonus episodes of Tuesday's sitcoms: Happy Endings (10:01/9:01c), in which Max and Penny kill Alex's racist parrot by accident; and Don't Trust the B---- in Apartment 23 (10:31/9:31c), where June starts a new job but Chloe, as usual, tries to put a mischievous damper on things. ... Jillian Michaels returns to help train the new cast of NBC's The Biggest Loser (8/7c), which for the first time includes kid contestants. ... Grey's Anatomy's T.R. Knight joins CBS' The Good Wife (9/8c) in a recurring role as a new adviser to Peter's campaign, while Michael J. Fox returns to mess with the firm, trying to block their latest payday. ... Recent Kennedy Center Honors recipient David Letterman opens up to Oprah Winfrey in a rare interview on Oprah's Next Chapter (OWN, 9/8c). ... Or you could watch Here Comes Honey Boo Boo (TLC, 9/8c) celebrate Halloween in a holiday special, in which we learn Mama June has a fear of mayonnaise. 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